1. Field of the Invention
This invention relates to a coating apparatus for coating a long object.
More specifically, this invention relates to a coating apparatus comprising a paint vessel having an opening at its bottom for passing of an object to be coated therethrough and a driving section for moving the paint vessel relative to the object, and further including a sealing member having excellent sealability provided below the opening of the paint vessel.
2. Description of the Prior Art
Heretofore, long articles have been coated by blade coating, for example by using a die, a roll, a brush, or a belt, or by passing such an article through a die having nearly the same outer shape as the article. With these methods, the speed of shearing becomes high during the coating operation, and it is difficult to obtain a relatively thick coated film uniformly. Furthermore, when the object to be coated has raised and depressed areas, a uniform film thickness is difficult to obtain.
It is also known to dip-coat a long article by utilizing a fixed vessel containing a coating agent. With this method, however, it is extremely difficult to coat articles which are very long, have a large weight, or are difficult to convey.
For this reason, a long article having a large weight has been coated by manual brush coating, for example by a manual operation conducted by a worker sitting on a chair suspended by a rope, or by a worker getting on a gondola. Such methods, however, can be unsafe when performed at high altitude, environmentally hazardous due to scattering of the coating solution is undesirable for environmental hygiene, and the working efficiency is low because of the manual operation.
The present inventors proposed in Japanese Laid-Open Patent Publication No. 150461/1983 (Japanese Patent Application No. 30584/1982) a coating apparatus suitable for coating a long article fixedly provided in the vertical direction, such as hanger ropes of a suspension bridge. This coating apparatus comprises a paint vessel having an opening at its bottom for passing of a coating object therethrough, and a driving section for moving the paint vessel relative to the coating object. This apparatus further includes a sealing member below the opening of the paint vessel, which is disposed rotatably in a holder and has a hole having a shape corresponding to the cross-sectional shape of an object.
This coating apparatus has excellent advantages. For example, it can coat a long article with good efficiency, but is still desired to be improved in many respects. For example, when irregularly raised and depressed portions exist on the surface of a coating object such as a hanger rope or the coating object varies in cross-sectional shape owing to multicoat coating, it is not always easy to make the inside surface of the sealing member conform to the outer shape of the hanger rope. If the hole of the sealing member is larger than the outer shape of the hanger rope, the paint tends to leak. If it is smaller, friction increases and a smooth descending motion becomes difficult.
Furthermore, when the material from which the sealing member is made is too hard, it injures the surface of the hanger rope or gets caught by the raised and depressed portions on the surface of the rope, and the motion of the coating apparatus might not be performed smoothly. On the other hand, if the sealing member is too soft, the rotating sealing member undergoes marked deformation in the vicinity of the periphery of the hanger rope and the clearance between the hanger rope and the sealing member increases. As a result, the coating solution tends to leak, and the selection of the material for the sealing member is difficult.
Furthermore, when the space between the sealing member and a holder therefor is too large, the coating solution tends to leak. If it is too narrow, the rotation of the sealing member is prevented and the coating apparatus does not operate smoothly. Hence, this space should be of a specified magnitude with a sufficient accuracy.